The polycondensation or polymerization of low molecular weight siloxanol oils has been practiced for several years. A wide range of catalysts have been used to perform these processes with a reasonable reaction time and temperature. Catalysts that may be used include, among others, sulfric acid, trifluorosulfonic acid, some Lewis acids, sodium or potassium hydroxide, tetrabutylphosphonium silanolate and some amines. A number of U.S. Patents disclose the use of phosphonitrilic compounds for the polycondensation and redistribution of low viscosity siloxane oligomers or polymers. In particular, U.S. Pat. Nos. 2,830,967; 3,186,967; 3,839,388; and 4,725,643. U.S. Pat. No. 4,975,510 discloses linear phosphonitrilic chlorides represented by the formula: EQU Cl.sub.3 P(NPCl.sub.2).sub.n NPCl.sub.3.sup.+PCl.sub.6 -
where n is an integer of from 1 to 6 are effective as catalysts for the polycondensation and equilibration of the low viscosity siloxane polymers. These catalysts have been shown to be especially effective for the production of siloxane fluids having a low content of terminal silanol groups. More recently U.S. Pat. Nos. 4,888,405 and 5,008,229 have disclosed new catalytic compositions containing phosphonitrilic chlorides and/or reaction products of these phosphonitrilic chlorides with organopolysiloxanes and/or organosilanes. A recent British Patent, 2,252,969 describes catalyst compounds having the general formula: EQU Cl.sub.3 P(NPCl.sub.2).sub.n NPCl.sub.3.sup.+ECl.sub.m -
where E is an element having an electronegativity value of from 1.2 to 2 such as Al, Sb, P, Sn, Zn and Fe. U.S. Pat. No. 5,403,909 discloses phosphonitrilic compounds of the formula: EQU O(X).sub.2-a Y.sub.a P(NPX.sub.2).sub.b NPX.sub.3-c Y.sub.c
where b is an integer ranging from 0 to 8, a is 0 or 1, c is 0 or 1, X is a halogen selected from the group consisting of fluorine, chlorine, bromine, and iodine, Y is selected from the group consisting of OH, OR' and R'CO.sub.2 where R' is alkyl or aryl; or EQU O(X).sub.2-a Y.sub.a P(NPX.sub.2).sub.b NP(O)X.sub.2-c Y.sub.c
where b is an integer ranging from 0 to 8, a is 0 or 1, c is 0 or 1, X is a halogen selected from the group consisting of fluorine, chlorine, bromine, and iodine, Y is selected from the group consisting of OH, OR' and R'CO.sub.2 where R' is alkyl or aryl as catalysts for the polycondensation and redistribution of siloxane polymers.
In spite of the foregoing developments, there is a continuing search for catalysts that are soluble in siloxanes, low in halogen content and active for the polymerization of organosiloxanes. It is known that the application of standard linear phosphonitrilic chlorides (LPNC's) as catalysts for polycondensation of low molecular siloxanediols can produce a high molecular gum which does not contain cyclic oligomeric siloxanes and that the gum can be prepared in a short cycle time. It is also known that a mixture of high molecular weight organopolysiloxanes and low molecular weight siloxanes can be redistributed into linear polymers without formation of a significant amount of cyclic species.